1. Field of the Invention
The present invention relates to a process for laminating a nanofiber web to a substrate, and to filters and laminates useful in filters for removing solids from fluid streams, as, for example, in industrial gas streams.
2. Discussion of Related Art
Dust collector or bag house type gas filtration is generally used to filter particulate material from industrial effluent or “off-gas,” as well as to collect fine product in particulate or powder form. A bag house structure generally includes one or more banks of flexible filter elements, commonly in the form of filter bags, supported within the structure. Filter bags have a generally sleeve-like tubular configuration, with gas flow through the bag house directed so as to deposit the particulate material being filtered during operation of the bag house on the exterior of the sleeve. Each filter bag is secured and maintained in a position such that gas can efficiently passes through the bag thereby removing entrained particulates. U.S. Pat. No. 4,983,434, hereby incorporated by reference, exemplifies a bag house filter structure and a filter for use therein. Dust collectors may also utilize filter elements in the form of cartridges having a generally tubular configuration (round or nonround) typically including pleated filter media. U.S. Pat. No. 5,632,791, hereby incorporated by reference, exemplifies a cartridge filter element.
During operation of the “bag house,” used herein to refer both to structures utilizing bags and structures utilizing cartridges, the filter elements (including bags and cartridges, herein referred to interchangeably as “elements” or “bags”) must be periodically cleaned when the pressure drop through the bag caused by accumulation of particulate becomes significant. One mode of cleaning bag house filters, referred to as “pulse jet” or “reverse pulse” cleaning is by subjecting the bags to a short burst of reverse-flow air that enters the interior of the filter bags and dislodges the filtered particulate material from the exterior of the bags for collection in the lower portion of the bag house. As the cleaning air passes through the tube venturi, it aspirates secondary air and the resulting air mass violently expands the bag and casts off the collected particulate matter (the “dust cake”). The bag will typically snap back to the cage support and the cleaned filter continues collecting particulate. Pulse jet is the most stressful type of cleaning on the bag house filter media itself, among both bag and cartridge type filters. When a laminate material is used as the media in a pulse jet type filter, the stress on the media caused by repeated expanding and retracting causes multilayered filter media to delaminate.
U.S. Pat. No. 6,740,142 discloses bag house filter media formed from a substrate at least partially covered by a layer of fine fibers having a diameter of between about 0.01 and about 0.5 micron, the fine fiber layer having a basis weight of 0.005 to 2.0 grams per square meter (gsm) and a thickness of 0.1 to 3 microns. To produce the filter media, it is disclosed in U.S. Pat. No. 6,740,142 that a web of nanofibers can be formed directly on the surface of the substrate.
The present invention is directed to a process for forming laminated filter media, and the laminated filter media made thereby. The resulting filter media are have improved resistance to delamination during use with reverse pulse cleaning, are highly efficient, easily cleaned, have the requisite strength characteristics and are economical to produce.